3 * Interface to GiNaC's special tensors. */
6 * GiNaC Copyright (C) 1999-2001 Johannes Gutenberg University Mainz, Germany
8 * This program is free software; you can redistribute it and/or modify
9 * it under the terms of the GNU General Public License as published by
10 * the Free Software Foundation; either version 2 of the License, or
11 * (at your option) any later version.
13 * This program is distributed in the hope that it will be useful,
14 * but WITHOUT ANY WARRANTY; without even the implied warranty of
15 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
16 * GNU General Public License for more details.
18 * You should have received a copy of the GNU General Public License
19 * along with this program; if not, write to the Free Software
20 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
23 #ifndef __GINAC_TENSOR_H__
24 #define __GINAC_TENSOR_H__
31 /** This class holds one of GiNaC's predefined special tensors such as the
32 * delta and the metric tensors. They are represented without indices.
33 * To attach indices to them, wrap them in an object of class indexed. */
34 class tensor : public basic
36 GINAC_DECLARE_REGISTERED_CLASS(tensor, basic)
42 // functions overriding virtual functions from bases classes
44 ex subs(const lst & ls, const lst & lr) const;
46 unsigned return_type(void) const { return return_types::noncommutative_composite; }
50 /** This class represents the delta tensor. If indexed, it must have exactly
51 * two indices of the same type. */
52 class tensdelta : public tensor
54 GINAC_DECLARE_REGISTERED_CLASS(tensdelta, tensor)
56 // functions overriding virtual functions from bases classes
58 void print(std::ostream & os, unsigned upper_precedence=0) const;
59 ex eval_indexed(const basic & i) const;
60 bool contract_with(exvector::iterator self, exvector::iterator other, exvector & v) const;
64 /** This class represents a general metric tensor which can be used to
65 * raise/lower indices. If indexed, it must have exactly two indices of the
66 * same type which must be of class varidx or a subclass. */
67 class tensmetric : public tensor
69 GINAC_DECLARE_REGISTERED_CLASS(tensmetric, tensor)
71 // functions overriding virtual functions from bases classes
73 void print(std::ostream & os, unsigned upper_precedence=0) const;
74 ex eval_indexed(const basic & i) const;
75 bool contract_with(exvector::iterator self, exvector::iterator other, exvector & v) const;
79 /** This class represents a Minkowski metric tensor. It has all the
80 * properties of a metric tensor and is (as a matrix) equal to
81 * diag(1,-1,-1,...) or diag(-1,1,1,...). */
82 class minkmetric : public tensmetric
84 GINAC_DECLARE_REGISTERED_CLASS(minkmetric, tensmetric)
88 /** Construct Lorentz metric tensor with given signature. */
89 minkmetric(bool pos_sig);
91 // functions overriding virtual functions from bases classes
93 void print(std::ostream & os, unsigned upper_precedence=0) const;
94 ex eval_indexed(const basic & i) const;
98 bool pos_sig; /**< If true, the metric is diag(-1,1,1...). Otherwise it is diag(1,-1,-1,...). */
102 /** This class represents the totally antisymmetric epsilon tensor. If
103 * indexed, all indices must be of the same type and their number must
104 * be equal to the dimension of the index space. */
105 class tensepsilon : public tensor
107 GINAC_DECLARE_REGISTERED_CLASS(tensepsilon, tensor)
109 // other constructors
111 tensepsilon(bool minkowski, bool pos_sig);
113 // functions overriding virtual functions from bases classes
115 void print(std::ostream & os, unsigned upper_precedence=0) const;
116 ex eval_indexed(const basic & i) const;
120 bool minkowski; /**< If true, tensor is in Minkowski-type space. Otherwise it is in a Euclidean space. */
121 bool pos_sig; /**< If true, the metric is assumed to be diag(-1,1,1...). Otherwise it is diag(1,-1,-1,...). This is only relevant if minkowski = true. */
126 inline const tensor &ex_to_tensor(const ex &e)
128 return static_cast<const tensor &>(*e.bp);
131 /** Create a delta tensor with specified indices. The indices must be of class
132 * idx or a subclass. The delta tensor is always symmetric and its trace is
133 * the dimension of the index space.
135 * @param i1 First index
136 * @param i2 Second index
137 * @return newly constructed delta tensor */
138 ex delta_tensor(const ex & i1, const ex & i2);
140 /** Create a symmetric metric tensor with specified indices. The indices
141 * must be of class varidx or a subclass. A metric tensor with one
142 * covariant and one contravariant index is equivalent to the delta tensor.
144 * @param i1 First index
145 * @param i2 Second index
146 * @return newly constructed metric tensor */
147 ex metric_tensor(const ex & i1, const ex & i2);
149 /** Create a Minkowski metric tensor with specified indices. The indices
150 * must be of class varidx or a subclass. The Lorentz metric is a symmetric
151 * tensor with a matrix representation of diag(1,-1,-1,...) (negative
152 * signature, the default) or diag(-1,1,1,...) (positive signature).
154 * @param i1 First index
155 * @param i2 Second index
156 * @param pos_sig Whether the signature is positive
157 * @return newly constructed Lorentz metric tensor */
158 ex lorentz_g(const ex & i1, const ex & i2, bool pos_sig = false);
160 /** Create an epsilon tensor in a Euclidean space with two indices. The
161 * indices must be of class idx or a subclass, and have a dimension of 2.
163 * @param i1 First index
164 * @param i2 Second index
165 * @return newly constructed epsilon tensor */
166 ex epsilon_tensor(const ex & i1, const ex & i2);
168 /** Create an epsilon tensor in a Euclidean space with three indices. The
169 * indices must be of class idx or a subclass, and have a dimension of 3.
171 * @param i1 First index
172 * @param i2 Second index
173 * @param i3 Third index
174 * @return newly constructed epsilon tensor */
175 ex epsilon_tensor(const ex & i1, const ex & i2, const ex & i3);
177 /** Create an epsilon tensor in a Minkowski space with four indices. The
178 * indices must be of class varidx or a subclass, and have a dimension of 4.
180 * @param i1 First index
181 * @param i2 Second index
182 * @param i3 Third index
183 * @param i4 Fourth index
184 * @param pos_sig Whether the signature of the metric is positive
185 * @return newly constructed epsilon tensor */
186 ex lorentz_eps(const ex & i1, const ex & i2, const ex & i3, const ex & i4, bool pos_sig = false);
190 #endif // ndef __GINAC_TENSOR_H__